hi, excuse me where did I mistake in these procedures? (I want to fit these models to my data) install.packages('drc',rep='http://cran.um.ac.ir') install.packages('car',rep='http://cran.um.ac.ir') install.packages('abind',rep='http://cran.um.ac.ir') library(car) library(abind) library(alr3) library(gtools) library(magic) library(plotrix) library(drc) library(lattice) library(MASS) library(nlme) library(methods) library(stats) library(stats4) dose<-c(0,1,2,3) SRMKN<-scan() 100 64.82649842 50.15772871 9.936908517 a=data.frame(dose,SRMKN) par(mfrow=c(3,3)) ##fit the logistic model## a.m1 <- drm(SRMKN ~ dose, data = a, fct = L.4()) summary(a.m1) plot(a.m1) logLik(a.m1) ED(a.m1, 50, interval='delta') ##fitting the linear model## a.m2<-lm(SRMKN ~ dose, data = a) plot(a.m2) ##fitting the quadratic model## a.m3<-lm(SRMKN ~ dose^2, data = a) plot(a.m3) [[alternative HTML version deleted]]